Soil Formation and Classification

These flashcards cover key vocabulary related to soil formation and classification based on lecture notes.

Weathering

The process of breaking down rocks into regolith.

Regolith

A layer of loose, heterogeneous material covering solid rock.

Soil Profile

The vertical section of soil that reveals all layers (horizons) of soil.

O Horizon

An organic horizon rich in decomposed material, typically found in forests.

A Horizon

The topmost mineral horizon, darkened by decomposed organic matter.

E Horizon

A horizon characterized by maximum leaching of minerals and clay.

B Horizon

A zone of accumulation where materials leached from above are deposited.

Albic Horizon (E)

A leached horizon containing little organic matter; often appears white.

Pedon

The smallest three-dimensional unit of soil that displays all individual characteristics.

Epipedons

Diagnostic surface horizons used to classify soils, including A and O horizons.

Endopedons

Diagnostic subsurface horizons used for soil classification.

Mollic Epipedon

A thick (at least 25cm), dark horizon rich in organic matter, high in bases

Umbric Epipedon

a dark horizon also rich in organic matter, but with low bases

Histic Epipedon

very dark and very high in organic matter, like peat or muck, thick (at least 10cm)

Ochric Epipedon

Thinner, lighter in color, lower in OM, or shallower than mollic or umbric

Albic (E)

E horizon, Maximum zone of eluviation, Albino, white

Cambic (Bw)

Weakly weathered or weakly developed, Usually only changes in color or structure (no accumulation)

Argillic Horizon (Bt)

A subsurface horizon characterized by an accumulation of clay with high bases

Kandic (Bt, Bts)

Accumulation of clays with low bases (e.g., kaolinite)

Spodic (Bh, Bhs)

Illuvial horizon with humus and Fe/Al oxides, Forms in highly leached forest soils of cool humid

climates, (easy to identify: Only dark/black horizon under E), usually buried

Oxic (Bo)

Illuvial zone of oxides, 1:1 clays and very few

weatherable minerals

Calcic (Bk)

calcium carbonates present

petrocalcic (Bkm)

calcium carbonate that is cemented

Gypsic (By)

gypsum

Petrogypsic (Bym)

gypsum that is cemented

Salic (Bz)

soluble salts

Natric (Btn)

clay with high levels of Na

Alfisol (alf)

argillic horizon, high bases

Entisol (ent)

VERY young, A and C horizons only, ochric surface horizon

Andisol (and)

Soil developed from volcanic materials, typically high in organic matter and mineral variation.

Aridisol (id)

dry climate, usually ochric

Gelisol (el)

Soil with a permanently frozen layer

Histosol (ist)

organic, at least a meter thick

Inceptisol (ept)

young soil, cambic horizon (Bw)

Mollisol (oll)

mollic epipedon, high bases, dark and soft

Oxisol (ox)

Oxic epipedon, highly weathered

Ultisol (ult)

Kandic horizon, low bases, moderately high weathering

Spodosol (od)

A soil with a spodic horizon, typically found in sandy, acid parent materials.

Vertisol (ert)

high in swelling clays, deep cracks when dry, slickensides, argillic or mollic horizons

Soil Moisture Regimes

Classes that describe the presence or absence of water in soil during certain periods.

aquic moisture regime

saturated with water, very poor aeration

Ustic Moisture regime

some plant-available moisture during growing season with significant periods of drought

Aridic Moisture Regime

Soils that are dry for at least half of the growing season.

Udic Moisture Regime

high moisture year round

Xeric Moisture regime

cool, wet winters and warm dry summers, seasonal rain

Subsidence

The gradual settling of the ground surface due to various factors.

Land Use Capability Classes

A classification system based on the suitability of land for various uses.

class (1-8) suitability for use or degree of hazard/limitation to land use

Class 1 (I) soils have few limitations that restrict their use. – Class 2 (II) soils have moderate limitations that reduce the choice of plants or that require moderate conservation practices. – Class 3 (III) soils have severe limitations that reduce the choice of plants or that require special conservation practices, or both. –… – Class 7 (VII) soils have very severe limitations that make them unsuitable for cultivation and that restrict their use mainly to

grazing, forestland, or wildlife habitat. – Class 8 (VIII) soils and miscellaneous areas have limitations that preclude commercial plant production and that restrict their use

to recreational purposes, wildlife habitat, watershed, or esthetic purposes.

Subclass - class plus type of management or conservation problem.

e – erosion

w – wet

s – root zone limitation such as bedrock (shallow)

c – climate